Présentations Colloques

Session 8.03: Geometrical structure and hydrogeological properties of Hard-Rock aquifers.
Gigleux (orateur)
Fractured-rock surficial aquifer studies with optical borehole-wall imaging in support of hydrogeology
Subject to licensing, Cigeo, a deep geological disposal facility for radioactive wastes will be built along the border of the Meuse and Haute-Marne departments in eastern France, where research conducted since the 1990s has identified a site with geology favourable to its siting. Cigeo will consist of an underground (about 500 m depth) facility in which packages of radioactive waste will be emplaced and surfaces facilities used to receive, inspect and prepare waste.**A comprehensive understanding of the shallow groundwater circulations in the outcropping “Calcaires du Barrois” formation (upper Kimmeridgian to lower Tithonian alternation of limestone and shale) is required for the setting of surface facilities and for the environmental impact assessment. Characterizing water storage and flows in these fractured and weathered limestones with a mechanistic approach depend on a good knowledge of the fracturation process. **Recent geotechnical campaigns, preliminary to the construction of surface facilities, gave us an opportunity to perform an intense set of logging on 21 core drilled boreholes associated to the piezometric monitoring with sample interval of 15' on 10 piezometers.**The combined application of optical imaging, core description, wireline logging (natural gamma-ray and imaging with optical borehole imager), seismic refraction and piezometric survey provides critical information for geometric modeling of geological units with emphasis on fracturated and weathered zone and for conceptual modeling of hydrodynamic model of the site.**As a perspective of this study, hydrogeological test monitoring, in-situ wells characterization and tracing experiments should provide further support of the interpretation of Magnetic Resonance Sounding.**